U.S. patent application number 10/911813 was filed with the patent office on 2005-02-17 for semiconductor substrate supporting apparatus.
This patent application is currently assigned to ASM JAPAN K.K./. Invention is credited to Shuto, Mitsutoshi, Suzuki, Yasuaki.
Application Number | 20050037626 10/911813 |
Document ID | / |
Family ID | 34131752 |
Filed Date | 2005-02-17 |
United States Patent
Application |
20050037626 |
Kind Code |
A1 |
Shuto, Mitsutoshi ; et
al. |
February 17, 2005 |
Semiconductor substrate supporting apparatus
Abstract
A semiconductor substrate supporting apparatus for supporting a
single semiconductor substrate in a plasma CVD apparatus comprises
a placing block having a substrate placing area on which the
substrate is placed. The substrate placing area is anodized and has
as an outermost film an anodic oxide film having a thickness of
about 30 .mu.m to about 60 .mu.m and/or a dielectric breakdown
voltage of about 300 V or higher.
Inventors: |
Shuto, Mitsutoshi; (Tokyo,
JP) ; Suzuki, Yasuaki; (Tokyo, JP) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Assignee: |
ASM JAPAN K.K./
Tokyo
JP
|
Family ID: |
34131752 |
Appl. No.: |
10/911813 |
Filed: |
August 5, 2004 |
Current U.S.
Class: |
438/765 |
Current CPC
Class: |
C23C 16/5096 20130101;
C23C 16/4581 20130101 |
Class at
Publication: |
438/765 |
International
Class: |
H01L 021/469 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 14, 2003 |
JP |
2003-293341 |
Claims
What is claimed is:
1. A semiconductor substrate supporting apparatus for supporting a
single semiconductor substrate in a plasma CVD apparatus,
comprising a placing block having a substrate placing area on which
the substrate is placed, said substrate placing area being anodized
and having as an outermost film an anodic oxide film having a
thickness of about 30 .mu.m to about 60 .mu.m.
2. The semiconductor substrate supporting apparatus according to
claim 1, wherein the anodic oxide film is constituted by aluminum
oxide.
3. The semiconductor substrate supporting apparatus according to
claim 1, wherein the placing block is constituted by aluminum or an
aluminum alloy.
4. The semiconductor substrate supporting apparatus according to
claim 1, wherein the anodic oxide film has a dielectric breakdown
voltage of about 300 V or higher.
5. The semiconductor substrate supporting apparatus according to
claim 1, wherein the anodic oxide film has a surface roughness of
about 3 .mu.m to 7 .mu.m.
6. The semiconductor substrate supporting apparatus according to
claim 1, further comprising a heating block on which the placing
block is mounted.
7. The semiconductor substrate supporting apparatus according to
claim 6, wherein the placing block has a thickness of about 5 mm to
about 15 mm.
8. The semiconductor substrate supporting apparatus according to
claim 1, wherein the placing block has a side surface which is
anodized and constituted by an anodic oxide film.
9. The semiconductor substrate supporting apparatus according to
claim 8, wherein the anodic oxide film of the side surface is
constituted by aluminum oxide and has a thickness of 30 .mu.m to 60
.mu.m.
10. The semiconductor substrate supporting apparatus according to
claim 1, wherein the placing block has an annular lip portion at
its periphery outside the substrate placing area.
11. The semiconductor substrate supporting apparatus according to
claim 10, wherein the annular lip portion is anodized and has an
anodic oxide film as an outermost film.
12. The semiconductor substrate supporting apparatus according to
claim 11, wherein the anodic oxide film in the lip portion has a
thickness of 30 .mu.m to 60 .mu.m.
13. A plasma CVD apparatus for processing a single substrate,
comprising a reaction chamber and the semiconductor substrate
supporting apparatus of claim 1 disposed in the reaction
chamber.
14. A method for forming a thin film on a substrate by plasma CVD,
comprising: providing the semiconductor substrate supporting
apparatus of claim 1; placing a substrate on the substrate placing
area of the placing block; and forming a thin film on the substrate
by plasma CVD, wherein plasma damage is controlled as a function of
the thickness of the anodic oxide film.
15. The method according to claim 14, wherein the dielectric
breakdown voltage of the anodic oxide film is about 300 V or
higher.
16. The method according to claim 14, wherein plasma damage is
further controlled as a function of the dielectric breakdown
voltage of the anodic oxide film.
17. A semiconductor substrate supporting apparatus for supporting a
single semiconductor substrate in a plasma CVD apparatus,
comprising a placing block having a substrate placing area on which
the substrate is placed, said substrate placing area being anodized
and having as an outermost film an anodic oxide film having a
dielectric breakdown voltage of 300 V or higher.
18. The semiconductor substrate supporting apparatus according to
claim 17, wherein the anodic oxide film is constituted by aluminum
oxide.
19. The semiconductor substrate supporting apparatus according to
claim 17, wherein the placing block is constituted by aluminum or
an aluminum alloy.
20. The semiconductor substrate supporting apparatus according to
claim 17, wherein the placing block has an annular lip portion at
its periphery outside the substrate placing area.
21. The semiconductor substrate supporting apparatus according to
claim 20, wherein the annular lip portion is anodized and has an
anodic oxide film as an outermost film.
22. A plasma CVD apparatus for processing a single substrate,
comprising a reaction chamber and the semiconductor substrate
supporting apparatus of claim 17 disposed in the reaction
chamber.
23. A method for forming a thin film on a substrate by plasma CVD,
comprising: providing the semiconductor substrate supporting
apparatus of claim 17; placing a substrate on the substrate placing
area of the placing block; and forming a thin film on the substrate
by plasma CVD, wherein plasma damage is controlled as a function of
the dielectric breakdown voltage of the anodic oxide film.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to a semiconductor
supporting apparatus for supporting a substrate inside a reaction
chamber in a thin-film formation apparatus; and particularly to a
semiconductor supporting apparatus which also serves as an
electrode inside a reaction chamber in a single-wafer-processing
type plasma CVD apparatus.
[0003] 2. Description of the Related Art
[0004] In conventional single-wafer-processing type plasma CVD
apparatuses, aluminum or aluminum alloy, which is light weight,
excels in thermal conductance and is less likely to cause
heavy-metal contamination, has been used as a material for a
semiconductor substrate supporting apparatus, which also serves as
an electrode. Because an aluminum or aluminum-alloy surface does
not always have satisfactory resistance to gas corrosion and
plasma, the surface may be anodized. Anodized aluminum or aluminum
alloy exhibits better protection from corrosion and plasma.
[0005] In conventional semiconductor supporting apparatuses,
however, the semiconductor apparatuses are frequently subject to
charge-up damage caused by a plasma. Even if anodized aluminum is
used, if charge-up on a semiconductor substrate surface increases,
leakage current occurs and a large amount of electrical charge
passes through the semiconductor apparatus. The semiconductor
apparatus may be damaged by leakage current. Leakage current means
the electric current caused by electrical charge accumulated on the
semiconductor apparatus passing to the grounding potential through
the semiconductor substrate supporting apparatus. If the leakage
current exceeds a given value, a gate insulation film of the
semiconductor apparatus and so forth are deteriorated or broken
down, lowering the yield of the semiconductor apparatus.
[0006] When surfaces of the conventional semiconductor supporting
apparatus are anodized, the anodized surfaces resist electrical
charge passing through the semiconductor substrate supporting
apparatus. If heated, however, stress caused by a difference
between linear thermal expansion coefficients of an aluminum alloy
base material and the anodized surface is produced, causing a crack
traversing through the anodized surface. This crack facilitates
flowing of electrical charge to the grounding potential through the
semiconductor substrate supporting apparatus, thereby causing a
leakage current increase.
[0007] As a countermeasure against these problems, a method using a
movable insulating plate was proposed (e.g., Japanese Patent
Laid-open No. 2002-134487). Using the insulating plate eliminates
leakage current because electric charge accumulated on the
semiconductor substrate does not pass through the semiconductor
substrate to the grounding potential.
[0008] Because thermal conductance is lowered if the insulating
plate is used, however, it takes time to raise a temperature of a
semiconductor substrate, thereby significantly lowering throughput.
Additionally, a substrate temperature becomes substantially lower
than a substrate temperature when the substrate is placed on a
surface-anodized supporting apparatus; if a heater temperature is
raised in order to increase a substrate temperature, temperature
control becomes difficult because a temperature difference between
a heater and the substrate is great. This makes it difficult to
control the properties of a film to be formed in a
single-wafer-processing type plasma CVD apparatus, thereby making
it impossible to manufacture a semiconductor apparatus as designed.
This is an extremely serious problem. Consequently, using the
above-mentioned insulating plate is not practical in the
single-wafer-processing type plasma CVD apparatus.
SUMMARY OF THE INVENTION
[0009] The present invention was achieved in view of one or more of
the above-mentioned problems. In an embodiment, an object of the
present invention is to provide an improved semiconductor substrate
supporting apparatus with small leakage current and an anodic oxide
film resisting dielectric breakdown.
[0010] Further, in another embodiment, an object of the present
invention is to provide a semiconductor substrate supporting
apparatus with excellent substrate temperature controllability and
high process stability.
[0011] In yet another embodiment, an object of the present
invention is to provide a semiconductor substrate supporting
apparatus which reduces charge-up damage and improves a yield of
processed substrates.
[0012] In still another embodiment, an object of the present
invention is to provide a semiconductor substrate supporting
apparatus which can be manufactured easily and at low cost.
[0013] In an additional embodiment, an object of the present
invention is to provide a plasma CVD apparatus comprising the
semiconductor substrate supporting apparatus and a method of using
the same, wherein plasma damage is effectively controlled.
[0014] The present invention is not intended to be limited by the
above objects, and various objects other than the above can be
accomplished as readily understood by one of ordinary skill in the
art.
[0015] In order to fulfill at least one of the above-mentioned
objects, in an embodiment, the present invention provides a
semiconductor substrate supporting apparatus for supporting a
single semiconductor substrate in a plasma CVD apparatus,
comprising a placing block having a substrate placing area on which
the substrate is placed, said substrate placing area being anodized
and having as an outermost film an anodic oxide film having a
thickness of about 30 .mu.m to about 60 .mu.m (including 35 .mu.m,
40 .mu.m, 45 .mu.m, 50 .mu.m, 55 .mu.m, and ranges between any two
numbers of the foregoing). In the above, the surface of the
substrate placing area is not only anodized but also accumulates a
depositing film up to at least about 30 .mu.m. When forming a thin
film on the substrate by plasma CVD, plasma damage can effectively
be controlled as a function of the thickness of the anodic oxide
film.
[0016] Further, to fulfill at least one of the aforesaid objects,
in an embodiment, the present invention provides a semiconductor
substrate supporting apparatus for supporting a single
semiconductor substrate in a plasma CVD apparatus, comprising a
placing block having a substrate placing area on which the
substrate is placed, said substrate placing area being anodized and
having as an outermost film an anodic oxide film having a
dielectric breakdown voltage of about 300 V or higher (including
350 V, 400 V, 450 V, 500 V, 600 V, 650 V, 700 V, 800 V, 1000 V, and
ranges between any two numbers of the foregoing). In the above, the
surface of the substrate placing area is not only anodized but also
accumulates a depositing film so as to provide a dielectric
breakdown voltage of about 300 V or higher. When forming a thin
film on the substrate by plasma CVD, plasma damage can effectively
be controlled as a function of the dielectric breakdown voltage of
the anodic oxide film.
[0017] The above embodiments can be combined and further each
include the following embodiments:
[0018] The anodic oxide film may be constituted by aluminum oxide.
The placing block may be constituted by aluminum or an aluminum
alloy. The placing block may have a side surface which is anodized
and constituted by an anodic oxide film. The side surface of the
placing block may not necessarily be provided with an anodic oxide
film in order to inhibit plasma damage or leakage current. The
anodic oxide film of the side surface may be constituted by
aluminum oxide and have a thickness thinner than that of the anodic
oxide film in the substrate placing area. In an embodiment, the
thickness of the anodic oxide film formed on the side surface may
be about 5 .mu.m to about 100 .mu.m, preferably nearly or
substantially the same as that of the anodic oxide film in the
substrate placing area.
[0019] The placing block may have an annular lip portion at its
periphery outside the substrate placing area. The annular lip
portion may be anodized and has an anodic oxide film as an
outermost film. The lip portion of the placing block may not
necessarily be provided with an anodic oxide film in order to
effectively inhibit plasma damage or leakage current. The anodic
oxide film of the side surface may have a thickness thinner than
that of the anodic oxide film in the substrate placing area. In an
embodiment, the thickness of the anodic oxide film formed in the
lip portion may be about 5 .mu.m to about 100 .mu.m, preferably
nearly or substantially the same as that of the anodic oxide film
in the substrate placing area. In an embodiment, the entire surface
of the placing block may be covered with an anodic oxide film
except for the bottom surface which may not be exposed to
plasmas.
[0020] The semiconductor substrate supporting apparatus may further
comprise a heating block on which the placing block is mounted. The
placing block may have a thickness of about 5 mm to about 15
mm.
[0021] In another aspect, the present invention provides a plasma
CVD apparatus for processing a single substrate, comprising a
reaction chamber and any one of the foregoing semiconductor
substrate supporting apparatus disposed in the reaction
chamber.
[0022] In still another aspect, the present invention provides a
method for forming a thin film on a substrate by plasma CVD,
comprising: (i) providing any one of the forgoing semiconductor
substrate supporting apparatus; (ii) placing a substrate on the
substrate placing area of the placing block; and (iii) forming a
thin film on the substrate by plasma CVD, wherein plasma damage is
controlled as a function of the thickness of the anodic oxide film
and/or a function of the dielectric breakdown voltage of the anodic
oxide film. Plasma damage can be controlled by correlating the
damage with the thickness of the anodic oxide film and/or the
dielectric breakdown voltage.
[0023] In the foregoing embodiments, any element used in an
embodiment can interchangeably be used in another embodiment, and
any combination of elements can be applied in these embodiments,
unless it is not feasible.
[0024] Plasma damage can occur due to various reasons including
uneven plasmas, current traversing a wafer laterally, and leakage
current. However, among them, leakage current is not well known. An
embodiment of the present invention focuses on leakage current.
Further, in an embodiment of the present invention, leakage current
can be significantly reduced by increasing a dielectric breakdown
voltage of the anodic oxide film. Further, in an embodiment of the
present invention, a dielectric breakdown voltage is increased by
increasing the thickness of the anodic oxide film.
[0025] A thick anodic oxide film may cause problems such as
increased susceptibility to thermal cracks or detachment and
gasification from the surface. In view of the above, the anodic
oxide film is formed on a surface of a placing block which supports
a single substrate and is disposed in a reaction chamber of plasma
CVD. In that case, unlike a thermal CVD apparatus or a batch type
plasma CVD apparatus, intense thermal cycles (such as repeating
temperature cycles between room temperature and several hundreds
centigrade) are not normally used in a single-wafer processing
plasma CVD apparatus. The temperature of the placing block is
nearly or substantially constant during plasma treatment. Thus, the
anodic oxide film may not be subject to thermal shock or stress,
and thus, even if the thickness of the anodic oxide film is great
such as 30 .mu.m or more, no degradation is likely to occur.
[0026] Additionally, in the case of a single-wafer processing
plasma CVD apparatus, during plasma treatment, the temperature of
the placing block is nearly or substantially constant, and when
plasma treatment is discontinued, the chamber is filled with inert
gas such as nitrogen (e.g., nitrogen gas flows through the
chamber). Thus, once the start-up is accomplished and the system is
stabilized, a gasification problem in that gas is generated and
released from a surface of a film is unlikely to be caused, even if
the thickness of the anodic oxide film is great such as 30 .mu.m or
more, no degradation is likely to occur.
[0027] For purposes of summarizing the invention and the advantages
achieved over the related art, certain objects and advantages of
the invention have been described above. Of course, it is to be
understood that not necessarily all such objects or advantages may
be achieved in accordance with any particular embodiment of the
invention. Thus, for example, those skilled in the art will
recognize that the invention may be embodied or carried out in a
manner that achieves or optimizes one advantage or group of
advantages as taught herein without necessarily achieving other
objects or advantages as may be taught or suggested herein.
[0028] Further aspects, features and advantages of this invention
will become apparent from the detailed description of the preferred
embodiments which follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] These and other features of this invention will now be
described with reference to the drawings of preferred embodiments
which are intended to illustrate and not to limit the
invention.
[0030] FIG. 1 is a schematic diagram of a plasma CVD apparatus
which includes the semiconductor substrate supporting apparatus
according to an embodiment of the present invention.
[0031] FIG. 2 is a partially enlarged cross section of a preferred
embodiment of the semiconductor substrate supporting apparatus
according to an embodiment of the present invention.
[0032] FIG. 3 is a graph showing the measurement results of leakage
current and dielectric breakdown voltage of the semiconductor
substrate supporting apparatus according to an embodiment of the
present invention.
[0033] Explanation of symbols used is as follows: 1: Plasma CVD
apparatus; 2: Reaction chamber; 3: Semiconductor substrate
supporting apparatus; 4: Showerhead; 5: Gas inlet pipe; 6: Heating
block; 7: Placing block; 8: Radio-frequency oscillator; 9:
Semiconductor substrate; 10: Matching circuit; 12: Opening portion;
13: Gate valve; 14: Exhaust port; 15: Piping; 16: Conductance
regulating valve; 17: Pressure controller; 18: Pressure gauge; 19:
Anodic oxide film; 20: Lip; 21: Supporting structure; 22: Heat
element; 23: Temperature controller; 24: Ground.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0034] As described above, the present invention includes various
embodiments including the following:
[0035] The semiconductor substrate supporting apparatus for
supporting a semiconductor substrate inside a reaction chamber in a
plasma CVD apparatus may comprise a placing block and a heating
block and is characterized in that top and side surfaces of the
placing block are anodized and a film thickness of an anodic oxide
film coated is approximately 30-60 .mu.m.
[0036] Specifically, the placing block may comprise an aluminum
alloy circular plate having a diameter of approximately 230-350 mm
and a thickness of approximately 5-15 mm. Preferably, the placing
block may have a lip portion at its periphery. Dielectric breakdown
voltage of the anodic oxide film coated is preferably about 300 V
or higher. In the above, the thickness of the anodic oxide film may
be nearly or substantially uniform or even throughout the substrate
placing surface in order to inhibit plasma damage attributable to
leakage current. The surface roughness of the anodic oxide film may
be of approximately 2-7 .mu.m in an embodiment. However, other
portions of the placing block may have various thicknesses of an
anodic oxide film.
[0037] In these embodiments, by making a film thickness of the
anodic oxide film thicker beyond an anodized surface to about 30-60
.mu.m, a dielectric breakdown voltage becomes preferably about 300
V or higher, thereby making it difficult that dielectric breakdown
occurs in the anodic oxide film during the plasma process.
Additionally, by making a film thickness of the anodic oxide film
thicker than the anodized surface, a resistance value of the anodic
oxide film becomes larger, thereby enabling to make leakage current
smaller. Furthermore, by making a film thickness of the anodic
oxide film thicker than the anodized surface, surprisingly, fewer
cracks occur; even if a crack occurs, it becomes difficult that the
crack reaches the aluminum alloy. As a result, it becomes possible
to reduce leakage current.
[0038] Because an insulating plate or another ceramic coating is
not used, controllability of a semiconductor substrate temperature
is excellent; and hence process stability is high.
[0039] Further, in an embodiment, charge-up damage is significantly
reduced, thereby enabling to improve the yield of the semiconductor
apparatus.
[0040] Additionally, in an embodiment, production costs of the
improved semiconductor supporting apparatus are inexpensive.
[0041] Preferred embodiments of the present invention will be
described with reference to drawings attached. The present
invention should not be limited to the preferred embodiments.
[0042] FIG. 1 is a schematic diagram of a single-wafer-processing
type plasma CVD apparatus which includes the semiconductor
substrate supporting apparatus according to an embodiment of the
present invention. The plasma CVD apparatus 1 comprises a reaction
chamber 2, a substrate supporting apparatus 3 disposed inside the
reaction chamber and used for placing a semiconductor substrate 9
on it, a showerhead 4 set up parallel to and facing the substrate
supporting apparatus 3 and used for emitting a jet of a reaction
gas uniformly onto the semiconductor substrate 9, an exhaust port
14 for evacuating the inside of the reaction chamber 2 and an
opening portion 12 for carrying in and out the semiconductor
substrate 9 to and from the reaction chamber 2.
[0043] As described below in detail, the substrate supporting
apparatus comprises a placing block 7 for placing the semiconductor
substrate 9 on it and a heating block 6 for heating the
semiconductor substrate 9. The placing block 7 is preferably an
aluminum alloy circular plate having a diameter of 230-350 mm and a
thickness of 5-15 mm; top and side surfaces of the circular plate
are coated with an anodic oxide film. The heating block 6 is
preferably an aluminum alloy cylinder having a diameter of 230-350
mm and a thickness of 20-100 mm and is integrated with a supporting
structure 21. The supporting structure 21 is grounded 24. The
substrate supporting apparatus 3 serves as one side of plasma
electrode. The supporting structure 21 is mechanically linked with
a drive mechanism (not shown in the figure) for moving the
substrate supporting apparatus 3 up and down. A
resistance-heating-type heat element 22 is laid buried inside the
heating block 6 and is connected to an external temperature
controller 23 and a power source (not shown). The heat element 22
is controlled by the temperature controller 23 and heats the
semiconductor substrate 9 at a given temperature (e.g.,
300-450.degree. C.).
[0044] The placing block is preferably constituted by aluminum.
Preferably, aluminum has a purity of 96% or higher. For example, as
aluminum, A5052 can be used which contains 0.25% or less of Si,
0.40% or less of Fe, 0.10% or less of Cu, 0.1% or less of Mn,
2.2-2.8% of Mg, 0.15-0.35% of Cr, 0.1% or less of Zn, 0.15% or less
of other metals, and the remaining of Al. A6061 also can be used
which contains 0.4-0.8% of Si, 0.7% or less of Fe, 0.15-0.40% of
Cu, 0.15% or less of Mn, 0.8-1.2% of Mg, 0.04-0.35% of Cr, 0.1% or
less of Zn, 0.15% or less of Ti, 0.15% or less of other metals, and
the remaining of Al.
[0045] The anodic oxide film is preferably constituted by aluminum
oxide such as Al.sub.2O.sub.3, which is formed by electrolysis on
an aluminum surface used as an anode in an electrolyte such as
sulfuric acid or oxalic acid, since the placing block is preferably
constituted by aluminum as described above. No restriction should
be imposed on formation processes of the anodic oxide film. The
thickness of an anodic oxide film depositing on an aluminum surface
by electrolysis can be determined based on the equation:
d=M/6F.rho..multidot.I.multidot.t, wherein d is thickness of a
depositing film, F is Faraday coefficient, .rho. is density of
Al.sub.2O.sub.3, M is molecular weight of Al.sub.2O.sub.3, I is
electric current, and t is time of passing the current. The actual
thickness of a depositing anodic oxide film may be slightly thinner
than the theoretical value due to a surface dissolving phenomenon
of the depositing anodic oxide film. In an embodiment, the
conditions of anodic oxidation may be as follows:
[0046] Electrolyte: approximately 10-20% of sulfuric acid solution;
Current density: D.C. approximately 1-2 A/dm.sup.2; Voltage:
approximately 10-20 V; Temperature: approximately 20-30.degree. C.;
Duration: approximately 20-60 min.; Thickness: approximately 30-60
.mu.m.
[0047] The bottom surface of the placing block may not be coated
with an anodic oxide film, which can be achieved by using a mask
such as an adhesive tape. Also, by covering the side surface of the
placing block, it is possible to form an anodic oxide film only on
the top surface of the placing block. Further, it is possible to
form an anodic oxide film only on a desired surface such as a
portion wherein a substrate is placed. The anodic oxide film needs
to be formed only on a surface such that an electrical charge does
flow through the substrate, although other surfaces can be coated
with an anodic oxide film.
[0048] The anodic oxide film having a thickness of about 30 .mu.m
to about 60 .mu.m has durability and may last until about
10,000-20,000 substrates are processed.
[0049] The showerhead 4 is connected to an external reaction gas
feed unit (not shown) through a gas inlet pipe 5. At an
undersurface 11 of the showerhead 4, thousands of fine pores (not
shown) for emitting a jet of reaction gas introduced via the gas
inlet pipe 5 onto the semiconductor substrate 9 are provided. The
showerhead 4 is electrically connected with radio-frequency
oscillators 8, 8' via a matching circuit 10 disposed outside the
reaction chamber and serves as the other side of plasma electrode.
The radio-frequency oscillators 8, 8' generate preferably two
different types of RF power of 13.56 MHz and 300-450 kHz
respectively. The two types of RF power are synthesized inside the
matching circuit 10 and applied to the showerhead.
[0050] The exhaust port 14 is linked with an external vacuum
exhaust pump (not shown) through piping 15 via a conductance
regulating valve 16. The conductance regulating valve 16 is
connected with a pressure gauge 18 and a pressure controller 17 and
controls a pressure inside the reaction chamber.
[0051] A gate vale 13 is provided at the opening portion 12; the
reaction chamber is linked with a transfer chamber (not shown) for
carrying in/out the semiconductor substrate 9 via the gate valve
13.
[0052] FIG. 2 is an enlarged cross section of a preferred
embodiment of the placing block 7 in the semiconductor substrate
supporting apparatus 3 according to an embodiment of the present
invention. The placing block 7 is a nearly circular plate
comprising aluminum alloy; its diameter is approximately 230-350
mm, preferably approximately 30-50 mm larger than a diameter of the
semiconductor substrate 9; its thickness is approximately 5-15 mm,
preferably approximately 7-12 mm. At the periphery of a top surface
of the placing block 7, a lip portion 20 is provided. The lip
portion 20 is formed so that a top surface 26 of the lip portion
becomes nearly or substantially the same height as a surface of the
semiconductor substrate 9 when the semiconductor substrate is
placed on a placing surface 25 of the placing block 7. In the case
of eight-inch wafers, the height may preferably be about 0.5 mm to
about 0.75 mm. The gap between the outer periphery of a wafer and
the inner periphery of the lip portion may preferably be about 1 mm
to about 2 mm. The lip portion 7 serves for preventing
concentration of plasma potential applied from the showerhead. The
placing surface 25 is formed to be a flat surface with preferably a
surface roughness Ra=5 .mu.m (in an embodiment, 1-20 .mu.m, 2-10
.mu.m, or 3-7 .mu.m) in the light of contamination prevention and
thermal conductivity.
[0053] The top (including the placing surface 25 and the top
surface 26 of the lip portion) and side surfaces 27 of the placing
block 7 are coated with an anodic oxide film 19 with a thickness of
preferably approximately 30-60 .mu.m, more preferably approximately
40-50 .mu.m. In the preferred embodiment shown in FIG. 2, although
an undersurface of the placing block 7 is not coated with the
anodic oxide film, it can be coated with the anodic oxide film with
the same thickness. As a modified version, the placing block can be
a simple circular plate not having a lip portion. Additionally, the
placing surface 25 can be a spot-faced concave shape, instead of a
flat surface. The present invention can be applied to placing block
in any shapes. The placing block 7 is removably screwed to the
heating block 6. Consequently, for example, by having placing
blocks coated with anodic oxide films of different thickness ready,
it is possible to use them according to process conditions. As an
alternative embodiment, the placing block and the heating block can
be integrally formed, instead of being removably fixed to each
other.
EXAMPLES
[0054] Measurements conducted for evaluating electrical
characteristics of the substrate supporting apparatus according to
an embodiment of the present invention are described below.
Measurements were made using the substrate supporting apparatuses
respectively having anodic oxide film thicknesses of 15 .mu.m, 30
.mu.m and 45 .mu.m. By placing an electrode with a diameter of 0.17
mm over the substrate supporting apparatus and by applying a
direct-current voltage of 0-1000 V, a leakage current and a voltage
generating dielectric breakdown were measured. Measurement results
of leakage current values and dielectric breakdown voltage values
are shown in Table 1. Incidentally, in this example, an IV
measuring instrument for measuring leakage current for wafers was
used, wherein instead of a wafer, a placing block was placed, and
instead of a film formed on the wafer, an anodic oxide film formed
on the placing block was analyzed.
1TABLE 1 Thickness of Leakage Current Value Dielectric Anodic Oxide
when 100 V voltage applied Breakdown Film (.mu.m) (x E .cndot. 08A)
Voltage Value (V) Comparative 5.77 173 Example (15) Example 1 (30)
4.38 337 Example 2 (45) 1.32 672
[0055] FIG. 3 is a graph made from the measurement results shown in
Table 1. As seen from the measurement results, when a film
thickness of an anodic oxide film coated on the substrate
supporting apparatus increases by twice the thickness of the
comparative example, a leakage current value decreases by 24%; when
a film thickness increases by three times the thickness of the
comparative example, a leakage current value decreases by 75%. This
is considered because a resistance value of the anodic oxide film
was increased as a film thickness was made thicker. Additionally,
when a film thickness of an anodic oxide film coated on the
substrate supporting apparatus increases by twice the thickness of
the comparative example, a dielectric breakdown voltage value
increases by approximately 1.9 times; when a film thickness
increases by three times the thickness of the comparative example,
a dielectric breakdown voltage value increases by approximately 3.9
times.
[0056] The results of actual film formation conducted using the
semiconductor substrate supporting apparatuses according to an
embodiment of the present invention are described below.
Measurements are made using the substrate supporting apparatuses
respectively having anodic oxide film thicknesses of 15 .mu.m and
30 .mu.m. After the film formation is finished, film properties of
a film formed including a film thickness, uniformity and stress
were examined. There were no changes observed between the films
formed and a film formed using a comparative substrate supporting
apparatus having an anodic oxide film thickness of 15 .mu.m.
[0057] Table 2 shows measurement results of the surface potential
(V), flat band potential (V) and interface state density
(pc./cm.sup.2.multidot.eV) of test wafers when a comparative
substrate supporting apparatus is used and when the substrate
supporting apparatus (a thickness of the anodic oxide film was 30
.mu.m) according to an embodiment of the present invention is used.
It was seen that values of interface state, flat band potential and
interface state density, which are indicators of the degree of
plasma damage, are extremely smaller when the substrate supporting
apparatus according to an embodiment of the present invention was
used than the values when the comparative substrate supporting
apparatus was used. This is considered because plasma damage was
decreased by using the substrate supporting apparatus according to
the embodiment of the present invention.
2 TABLE 2 Interface State Surface Flat Band Density Potential (V)
Voltage (V) (pc./cm.sup.2 .cndot. eV) Comparative 1.45 -4.1 1.3
.times. 10.sup.11 Example Embodiment of 0.60 -0.8 1.1 .times.
10.sup.11 Present Invention
[0058] Consequently, from the above measurement results, a film
thickness of the anodic oxide film of 30 .mu.m or more and
dielectric breakdown voltage of 300 V or higher are preferable for
the substrate supporting apparatus according to an embodiment of
the present invention.
[0059] This application claims priority under 35 U.S.C. .sctn. 119
to Japanese patent application No. 2003-293341, filed on Aug. 14,
2003, the disclosure of which is incorporated herein by reference
in its entirety.
[0060] It will be understood by those of skill in the art that
numerous and various modifications can be made without departing
from the spirit of the present invention. Therefore, it should be
clearly understood that the forms of the present invention are
illustrative only and are not intended to limit the scope of the
present invention.
* * * * *